This decision allows construction to continue on schedule. Work on the $1.5 billion, 6.6-mile Phase 2 extension is well underway along the entire alignment, with bridge and station work progressing quickly and trackwork starting soon.

"We appreciate the CPUC's diligence in reviewing the crossings for the Expo Line. Today's decision allows us to remain focused on completing the Expo Line in 2015 and bringing a new transit option to Los Angeles," said Expo Construction Authority CEO Rick Thorpe.

Service on Phase 1 of the Expo Line began in Spring 2012 and serves nearly 27,000 daily riders. Construction on Phase 2 is expected to be complete in late 2015. The Expo Line will bring greater mobility to the region by connecting west Los Angeles to the region's existing rail network.

This is the second legal hurdle the Expo Line has cleared in two weeks. Earlier this month, the California Supreme Court affirmed a court of Appeals ruling that the Expo Line Construction Authority does not have to redo any part of its environmental study for work to continue on the project.